To improve our understanding of the effects of tree species selection and management intensity on dissolved organic matter (DOM), we studied solution samples along the water flow path through forests with spectroscopic methods and biodegradation tests. There are distinct changes in DOM composition and biodegradability following the water path. Aboveground DOM was influenced by tree species selection but not by management intensity. Differences became aligned in mineral soil.

Experimental evidence from a network of 40 monitoring sites in Europe suggests that atmospheric nitrogen deposition to forests and other semi-natural vegetation impacts the carbon sequestration rates in ecosystems, as well as the net greenhouse gas balance including other greenhouse gases such as nitrous oxide and methane. Excess nitrogen deposition in polluted areas also leads to other environmental impacts such as nitrogen leaching to groundwater and other pollutant gaseous emissions.

Nitrogen deposition from the atmosphere to unfertilized terrestrial vegetation such as forests can increase carbon dioxide uptake and favour carbon sequestration by ecosystems. However the data from observational networks are difficult to interpret in terms of a carbon-to-nitrogen response, because there are a number of other confounding factors, such as climate, soil physical properties and fertility, and forest age. We propose a model-based method to untangle the different influences.

To improve our understanding of the effects of tree species selection and management intensity on dissolved organic matter (DOM), we studied solution samples along the water flow path through forests with spectroscopic methods and biodegradation tests. There are distinct changes in DOM composition and biodegradability following the water path. Aboveground DOM was influenced by tree species selection but not by management intensity. Differences became aligned in mineral soil.

Soil aggregate stability and POM occlusion are integral markers for soil quality. Besides physico-chemical interactions, biofilms are considered to aggregate primary particles, but experimental proof is still missing. In our experiment, soil aggregate samples were treated with biofilm degrading enzymes and showed a reduced POM occlusion and an increased bacteria DNA release compared with untreated samples. Thus, biofilms are assumed to be an important factor of POM occlusion in soil aggregates.

In a field experiment in Tanzania, we used substrates from local projects as soil amenders for intercropping relevant local crops, aiming to advance the practical application of known principles for smallholder agriculture in SSA, i.e. biochar and biogas application and EcoSan practices. We studied the short-term effects on crop productivity, plant nutrition and soil properties. By mitigating P scarcity and acidification, yields were increased by up to 400 % compared to the control.

Soil microbial biofilms are supposed to increase agglomeration of soil particles and therefore reduce erodibility. After inoculation with two strongly differing microbial communities, a sandy agricultural soil did not develop significant differences in aggregate stability. This leads to the assumption that mechanical properties of biofilms do not vary considerably across different biological/chemical compositions, which implies that aggregate stability is a resilient factor of soil fertility.

Climate and hydrology are relevant control factors determining the timing and amount of nutrient losses from land to aquatic systems, in particular of phosphorus (P) from agricultural lands. The main objective of the study was to evaluate the differences in P export patterns and the performance of alternative monitoring strategies in streams under contrasting climate-driven flow regimes: temperate and stable discharge conditions (Denmark) and sub-tropical and flashy conditions (Uruguay).

The hadal zone (6–11 km depth) is the least explored habitat on Earth. We studied microbial branched glycerol dialkyl glycerol tetraethers (brGDGTs) in the Challenger Deep, Mariana Trench. One unique feature is the strong predominance of 6-methyl brGDGT, which likely reflects an adaption of brGDGT-producing bacteria to alkaline seawater and low temperature. BrGDGTs, with elemental and isotopic data, suggest an autochthonous product for brGDGT. A new approach is proposed for brGDGT sourcing.

Biogeochemical processes of SOM are key for greenhouse gas emission and water quality. We extracted SOM by water or by NaOH–HCl under oxic–anoxic conditions. Chemical and anoxic extractions lead to higher SOM electron exchange capacities, resulting in stimulation of microbial Fe(III) reduction. Therefore, aqueous pH-neutral SOM extracts should be used to reflect environmental SOM redox processes, and artifacts of chemical extractions need to be considered when evaluating SOM redox processes.

Today, sterols are widespread in plants, animals, and fungi but are almost absent in the oldest rocks. Microbial mats, representing the earliest complex ecosystems on Earth, were omnipresent in Precambrian marine environments and may have degraded the sterols at that time. Here we analyze the distribution of sterols through a microbial mat. This provides insight into how variations in biological and nonbiological factors affect the preservation of sterols in modern and ancient microbial mats.

This study deals with two membrane lipids called BDGTs and PDGTs. Membrane lipids are molecules forming the cell envelope of all organisms. Different organisms produce different lipids thus they can be used to detect the presence of specific organisms in the environment. We analyzed the structure of these new lipids and looked for potential producers. We found that they are likely made by microbes emitting methane below the sediment surface and could be used to track these specific microbes.

Our understanding of terrestrial organic matter (TOM) in tropical peat-draining rivers remains limited, especially in Southeast Asia. We explored the characteristics of TOM via bulk parameters and lignin phenols of sediment in Malaysia. This showed that the most important plant source of the organic matter in these rivers is woody angiosperm C3 plants with limited diagenetic alteration. This slower degradation of TOM may be a link to higher total nitrogen content, especially for the small river.

Carbon dioxide concentrations (pCO2) in the atmosphere play an integral role in Earth system dynamics, especially climate. Past climates help us understand future ones, but reconstructing pCO2 over the geologic record remains a challenge. This research demonstrates new approaches for exploring past pCO2 via the carbon isotope fractionation in general algal lipids, which we test over a high CO2 gradient from a naturally occurring CO2 seep.

Samples were collected in August 2016 in the Rajang river and estuary, with tropical forest in its river basin and peatland in the estuary. Organic matter composition was influenced by transportation in the river basin, whereas peatland can added clear bio-degraded part to the fluvial organic matter, which implies modification of the initial lability and/or starting points in subsequent degradation/alternation process after the organic matter entering into the sea.

We found that peatlands in coastal Sarawak, Borneo, export extremely humified organic matter, which dominates the riverine organic matter pool and conservatively mixes with seawater, while the freshly produced fraction is low and stable in concentration at all salinities. We estimated that terrigenous fractions, which showed high photolability, still account for 20 % of the coastal dissolved organic carbon pool, implying the importance of peat-derived organic matter in the coastal carbon cycle.

High primary production in the Peruvian upwelling system is followed by rapid heterotrophic utilization of organic matter and supports the formation of one of the most intense oxygen minimum zones (OMZs) in the world. Here, we estimated vertical fluxes of oxygen and dissolved organic matter (DOM) from the surface to the OMZ. Our results suggest that DOM remineralization substantially reduces oxygen concentration in the upper water column and controls the shape of the upper oxycline.

We investigate the composition and vertical fluxes of POM in two deep basins of the Baltic Sea (GB: Gotland Basin and LD: Landsort Deep). The two basins showed different O2 regimes resulting from the intrusion of oxygen-rich water from the North Sea that ventilated the deep waters in GB, but not in LD.
In GB, O2 intrusions lead to a high abundance of manganese oxides that aggregate with POM, altering its composition and vertical flux and contributing to a higher POC transfer efficiency in GB.

Many marine microorganisms produce polysaccharide-rich transparent exopolymer particles (TEPs) for rather unknown reasons but with important consequences for the ocean carbon cycle, sea–air gas exchange and formation of organic aerosols. Here we compare surface–ocean distributions of TEPs and physical, chemical and biological variables along a N–S transect in the Atlantic Ocean. Our data suggest that phytoplankton and not bacteria are the main TEP producers, and solar radiation acts as a sink.

We explored the relationship between chemical composition and the temperature sensitivity of moss decomposition using 959-day lab incubations. Mass loss was low despite the predominance of carbohydrates, indicating the persistence of labile C. Scanning electron microscopy revealed little change in the moss cell-wall structure. These results suggest that the moss cell-wall matrix protects labile C from decomposition, contributing to the globally important stocks of moss-derived C.

With global warming, thawing of permafrost releases dissolved organic matter (DOM) into streams. By analyzing DOM along an alpine stream on the Qinghai–Tibet Plateau, we found DOM was mainly from the active layer, but with deepening of the active layer, the contribution of the deep permafrost layer increased, causing a change in the chemical composition of DOM. From the head- to downstream, DOM is undergoing rapid degradation, but some components are persistent and can be transported downstream.

We tried to identify the microbes which biosynthesize a class of lipids widespread in seawater, the long chain alkyl diols (LCDs). We could not find any microorganism likely involved in the production of LCDs. The amounts of LCDs found are too high to be produced by living organisms and are likely to be part of the refractory organic matter persisting for long periods in the water column.

Long-chain diols (LCDs) are biomarkers that occur widespread in marine environments and also in lakes and rivers. In this study, we looked at the distribution of LCDs in three river systems (Godavari, Danube, and Rhine) in relation to season, precipitation, and temperature. We found out that the LCDs are likely being produced in calm areas of the river systems and that marine LCDs have a different distribution than riverine LCDs.

In this study, we systematically analyze leaf wax derived n-alkane patterns in eastern Georgia to test their potential for paleoenvironmental reconstructions in the semi-humid to semi-arid central southern Caucasus region. We investigated the influence of vegetation types on the leaf wax signal in modern plants and topsoil material. Our results show distinct and systematic differences in the n-alkane patterns between vegetation types and prove their potential for vegetation reconstructions.

Sinking phytoplankton from the surface ocean provide the principal energy source to deep-ocean ecosystems. Our aim was to understand how different phytoplankton communities impact the chemical nature of this sinking material. We show certain types of phytoplankton can preferentially export energy-rich storage compounds to the seafloor. Any climate-driven effects on phytoplankton community structure could thus impact remote deep-ocean ecosystems thousands of kilometres beneath the surface.

Karst is a kind of typical calcium-rich environment, which is widely distributed. We measured the Ca2+ content of 41 plant species, as well as soil total Ca2+ and exchange Ca2+. We found out that different plants have different ways to high Ca2+ adaptation. According to the different high Ca2+ adaptation of the 17 dominant species, we divided them into 3 categories: Ca-indifferent plants, high-Ca plants and low-Ca plants. Our results can provide a theoretical basis for vegetation restoration.

Climate warming in the Arctic results in thawing of permafrost deposits. This promotes the accessibility of freeze-locked old organic matter (OM) accumulated during the past. Characterizing OM of different depositional ages, we were able to show that OM from last glacial Yedoma deposits possess the highest potential to provide organic substrates such as acetate for microbial greenhouse gas production and therefore to accelerate the carbon–climate feedback cycle during ongoing global warming.

The latitudinal dependency of POC / PON in ocean and inland water is significant, regulated by trophic state and climate, etc. factors. POC / PON significantly increased from coastal water (6.89 ± 2.38) to open ocean (7.59 ± 4.22) with the increasing rate of 0.0024 / km. The re-examination of the global relationship between, and variations in, POC and PON could be important for the global and regional coupling between the carbon and nitrogen cycles in the ocean and freshwater.

Associations between diatoms and N-fixing cyanobacteria (diatom–diazotroph associations, DDAs) play an important role in the N cycle of the tropical North Atlantic. Heterocysts are the site of N fixation and contain unique glycolipids. We measured these glycolipids in the water column and surface sediment from the tropical North Atlantic. We found a significant correlation between the concentration of glycolipid and of DDAs, strengthening their application as biomarkers.

The source of particulate organic matter in headwaters during storm events remains an open question. We use the molecular composition of organic matter sampled during four spring–summer storms and compare it to potential sources. We identify litter, streambed and vicinal soils as the main sources of particulate organic matter. Their proportions depend on (i) the size of the catchment and (ii) the rain event.

Plant carbon (C) content is critical to the assessment of the global C cycle. Our results showed that the global average C contents in organs were significantly lower than a canonical value of 50 %. Plant C content tended to decrease with increasing latitude, and life form explained more variation than climate. Our findings suggest that specific C content values of different organs and life forms should be incorporated into the estimations of regional and global vegetation biomass C stocks.

The Baltic Sea is characterized by recurring summer phytoplankton blooms, dominated by a few cyanobacterial species. These bacteria are able to use dinitrogen gas as the source for nitrogen and produce very specific lipids. We analyzed these lipids in a sediment core to study their presence over the past 7000 years. This reveals that cyanobacterial blooms have not only occurred in the last decades but were common at times when the Baltic was connected to the North Sea.

The balance between organic matter (OM) fixation and decay is a major control on atmospheric CO2 concentrations. Understanding the environmental, chemical, and physical mechanisms that control the distribution of OM decay rates is therefore critical for constraining the global carbon cycle. In this manuscript, we derive a method to relate OM reactivity to its isotope composition using a kinetic model and provide a novel framework to discern the controls on OM decay rates.

The results of this study highlight the changes of DOM composition in soil solutions and surface runoff, probably controlled by water-table dynamics and pre-event hydrological conditions. These changes should be taken into account for a better understanding of micropollutant mobility. Moreover, this work has implications for modeling DOM export in headwater catchments, as many studies assume that DOM transfer during storm events consists of the flushing of pre-existing soil solution DOM.

Neutral carbohydrates, carbon isotopic composition, and algal productivity proxies in three reservoir sediment cores, South China, were investigated. Monosaccharide compositions and diagnostic parameters indicate a predominant contribution of phytoplankton in the sediment cores. Algal monosaccharide content is highly related to the algal productivity and increasing mean air temperature, but not to nutrient input, demonstrating the effect of climate warming in low-latitude regions.

Leaf scale measurements have been performed on English oak, European beech and Norway spruce at a field site in Denmark to study the release of volatile compounds in response to a change in light. Whilst some compounds, like isoprene and sabinene, increased with increasing light, other compounds, like camphene, showed no light response for most of the trees. This can help to increase our knowledge of how species and compounds respond to light and to possibly improve how they can be modeled.

To better understand the role of oxygen for the biological carbon pump, we studied particle fluxes through hypoxic waters in the eastern tropical North Atlantic. Attenuation of organic carbon fluxes over depth was lower than expected from seawater temperatures, indicating co-effects of oxygen concentration. Differences were observed for individual organic components, suggesting that future carbon export fluxes may depend on changes in surface ocean organic matter quality under global change.

In this study, we demonstrated that the composition of sediment organic matter can vary significantly within a single lake, in a close relationship with the spatial patterns of elemental inorganic geochemistry. This results from a combination of different bio-, geo- and physicochemical lake factors, and our results highlight that the potential for large spatial variability across lakes should be considered when studying carbon, nutrient and trace element cycling at lake and global scales.

The biological carbon pump (BCP) plays a key role in regulating atmospheric CO2. Controls on the efficiency at which this occurs are poorly known. Here we combine in situ observations with an ecosystem model to show that zooplankton have an important role in regulating the efficiency of the BCP. Predicted future changes in ocean conditions, such as expansion of oxygen minimum zones, may decrease the role of zooplankton in the BCP globally, increasing its efficiency and altering atmospheric CO2.

Fluvial discharge and coastal erosion of the permafrost-dominated East Siberian Arctic delivers large quantities of terrigenous organic carbon (Terr-OC) to marine waters. We assessed its fate and composition in different marine pools with a suite of biomarkers. The dissolved organic carbon is transporting off-shelf “young” and fresh vascular plant material, while sedimentary and near-bottom particulate organic carbon preferentially carries old organic carbon released from thawing permafrost.

English oak and European beech are common European trees known to release volatile compounds such as isoprene and monoterpenes. By doing leaf chamber measurements at three sites in Europe, the aim was to study how the emission differed for cloned trees growing at different sites. The measured emission rates from clones varied between sites, but the relative compound contribution was stable both within and between sites. This can help to increase our knowledge of emission pattern variability.

Thawing permafrost may release large amounts of terrestrial organic carbon (TerrOC) to the Arctic Ocean. We assessed its fate in the marine environment with a suite of biomarkers. Across the Laptev Sea their concentrations in surface sediments decreased significantly and showed a trend to qualitatively more degraded TerrOC with increasing water depth. We infer that the degree of degradation of TerrOC is a function of the time spent under oxic conditions during protracted cross-shelf transport.

The Arctic contains a large pool of carbon that is vulnerable to warming and can be released by rivers and coastal erosion. We study microbial lipids (BHPs) in permafrost and shelf sediments to trace the source, transport and fate of this carbon. BHPs in permafrost deposits are released to the shelf by rivers and coastal erosion, in contrast to other microbial lipids (GDGTs) that are transported by rivers. Several further analyses are needed to understand the complex East Siberian Shelf system.

We present in this study a highly diverse and complex chemodiversity of dissolved organic matter (DOM) in the Amazon Basin analyzed by modern ultrahigh-resolution mass spectrometry and optical property analyses. DOM within the Rio Madeira (white water), Rio Negro (black water) and Rio Tapajós (clear water) area showed a large overlap of thousands of molecular formulae, but also unique signatures were apparent for each region, with significant correlations to colored DOM.

We use a novel ion chromatographic analysis that provides the first identification and quantification of major low-molecular-weight dissolved organic carbon (LMW-DOC) compounds in basal ice. LMW-DOC concentrations were dependent on the bioavailability of the overridden organic carbon, which in turn was influenced by the type of overridden material. The overridden material may thus act as a direct (abiotic leaching) and indirect (microbial cycling) source of DOC to the subglacial environment.

In the framework of the VAHINE project, we investigated the spectral characteristics and the variability of dissolved and particulate chromophoric materials throughout a 23-day mesocosm experiment conducted in the south-west Pacific at the mouth of the New Caledonian coral lagoon. We found that the dynamics of CDOM and particulate matter absorption were strongly coupled with those of cyanobacteria Synechococcus spp. and bacterial production.

In this study we investigated marine algae as a source of CH4 in oxic surface waters of oceans. Algae-derived CH4 may explain the CH4 oversaturating state within the surface mixed layer, sometimes also termed the "oceanic methane paradox".
This finding of an overlooked source of CH4 in marine environments will be of considerable importance to scientists in many disciplines because algae play a crucial role in organic matter cycling in marine and freshwater ecosystems.

Wetlands commonly feature high levels of natural dissolved organic matter (DOM), a critical component in their biogeochemical functions. Here we describe the first detailed, comparative, molecular characterization of DOM in three sub-tropical, pulsed, wetlands, using optical properties, high field nuclear magnetic resonance and ultrahigh resolution mass spectrometry, and compare compositional features to variations in organic matter sources and flooding characteristics.

Drifting sediment traps were deployed in the oxygen-deficient waters of the Arabian Sea, where the sinking flux is less attenuated than in more oxic waters. Six mechanisms that might explain this "enhanced flux" were evaluated using literature and data. In the upper 500 m, evidence was found supporting an oxygen effect and/or changes in the efficiency of the microbial loop, including the addition of chemoautotrophic carbon to the sinking flux.

Our results of this study show that two humic-like C peaks and two protein-like B and T peaks were identified from CDOM using PARAFAC for investigated lakes. The average fluorescence intensity of the components differed seasonally. Components 1 and 2 exhibited strong linear correlation (R2 = 0.63). Significantly positive linear relationships, between aCDOM and Fmax, and between DOC and salinity (R2 = 0.93), were revealed.

We studied tree and grass litter decomposition across several climates in Europe. Climatic (air temperature, precipitation and soil water content) controls on litter decomposition were quantitatively more important than species or site of origin. The data were used to generate prediction models of remaining litter mass, and carbon and nitrogen contents during the decomposition period. We also observed a significant drop in remaining litter mass after the first couple of days of decomposition.

This research reports a test of the applicability of three organic-derived temperature proxies (UK'37, TEX86 and LDI) at high latitudes around Iceland. A range of samples including suspended particular material (SPM), trapped descending particles and surface sediments were collected to test the different proxies in the water column and the sediment.The combination of three independent SST organic proxies provided important information about seasonality and differences in habitat depth.

Freezing can affect dissolved organic matter properties and concentrations. Nevertheless, water samples are regularly frozen for sample preservation. To test, if fast-freezing with liquid nitrogen instead of normal freezing at −18 °C can prevent changes in DOM characteristics, we compared fresh and differently frozen terrestrial water samples. We found that fast-freezing with liquid nitrogen can prevent bulk organic matter concentrations but not its spectroscopic properties.